Messages in this thread | | | Date | Thu, 30 Jun 2005 12:32:05 +0200 | From | Ingo Molnar <> | Subject | Re: PREEMPT_RT and I-PIPE: the numbers, take 3 |
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* Kristian Benoit <kbenoit@opersys.com> wrote:
> This is the 3rd run of our tests.
i'm still having problems reproducing your numbers, even the 'plain' ones. I cannot even get the same ballpark figures, on 3 separate systems. To pick one number:
> "plain" run: > > Measurements | Vanilla | preemp_rt | > ---------------+-------------+----------------+ > mmap | 660us | 2867us (+334%) |
i was unable to reproduce this level of lat_mmap degradation. I do indeed see a slowdown [*], but nowhere near the 4.3x slowdown measured here. I have tried the very lmbench version you used (2.0.4) on 3 different systems (Athlon64 2GHz, Celeron 466MHz, Xeon 2.4GHz - the last one should be pretty similar to your 2.8GHz Xeon testbox) and neither showed this level of slowdown.
i couldnt figure out which precise options were used by your test, because i only found the summary lmbench page of one of the older tests - so i did my lat_mmap testing with various sizes: 10MB, 30MB, 70MB, 150MB, 200MB, 500MB. (My best guess would be that since your target box has 512MB of RAM, lmbench will pick an mmap-file size of 144 MB. Or if it's the 256MB box, lmbench will pick roughly 70 MB. I covered those likely sizes too.) Neither size showed this level of slowdown.
so my tentative conclusion would be that the -RT kernel is still misconfigured somehow. Did you have HIGHMEM64 and HIGHPTE enabled perhaps? Those i suggested to be turned off in one of my first mails to you, it is something that will cause bad performance under PREEMPT_RT. (Highmem64 is unwarranted for an embedded test anyway - it's only needed to support more than 4 GB of RAM.) Could you send me the test 3 .config you used on the -RT kernel?
Ingo
[*] fixed in -50-36 and later PREEMPT_RT kernels - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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